if you plan on adding a battery to the system, here's a couple things to consider.
The stator output is AC, a battery is DC. You will have to add a rectifier to change the output to DC, and this will use up avaiable watts. I have been told you could lose 10-15 watts by using a rectifier. (I'm not THAT much of an electronics wizz, so I'm not sure on that point - just what I was told)
Depending on the rectifier, that could be true.
Alternating current is called that because the current reverses polarity as the magnets pass over the coils. The voltage is then shown as a wave with a peak positive voltage, falling to zero, then dipping to the same voltage negative, then back to positive again. Hook this up to a battery and for every amp you put in, you take it right back out again when the poles reverse. So, you need a rectifier to make all the voltage go the same way.
The simple way is the half wave rectifier, which need be nothing more than a single diode. This will simply cut off the voltage with the wrong polarity and let the rest through, but in so doing, you discard half of the current the magneto produces, and you loose a small amount more in ordinary losses.
Full wave rectifiers are a little more complicated, but not at all impractical. It passes the right way voltage, then "flips over" the wrong way voltage, and far less is lost.
Read (first half of the page is all that's necessary):http://en.wikipedia.org/wiki/Rectifier